This invention relates generally to a binocular stereoscopic viewing device, and in particular, to a binocular ophthalmoscope having a tilting mirror for directing light from a source of light toward the eye of a patient for stereoscopic observation of the latter.
A binocular ophthalmoscopic for indirect observations of a patient's eye includes an illumination unit connected to an observation unit. The observation unit deflects two observation beams and represents the optical path for observing the patient's eye. The illumination beam provided by the illumination unit represents the optical path for illuminating the patient's eye. The illumination and observation beams are directed from the ophthalmoscope to the eye of the patient. For optimum stereopsis, the two observation beams must be separated from each other as far as possible while falling within the pupil of the eye to be examined. The illumination beam, which must also strike the pupil of each eye to be examined, should be separated as far as possible from the images of the examiner's pupils.
Preferably, the illumination beam and two observation beams are separated as far as possible from each other within each eye to be examined by dilating each pupil to be examined through the application of a drug. Dilation of a patient's eye at times may not be possible or practical.
A first type of conventional binocular indirect ophthalmoscope (BIO), such as disclosed in U.S. Pat. No. 4,684,227, adjusts the observation and illumination beams for stereoscopic viewing by mounting on a common platform two mirrors for reflecting the two observation beams and a third mirror for reflecting the illumination beam. The platform is moved towards or away from the patient's eye in positioning the three beams within the patient's retina.
The BIO of U.S. Pat. No. 4,684,227 is well suited for observing portions of the patient's eye which are substantially at or near the center of the eye. When peripheral portions of the retina are to be examined such as, but not limited to, the upper portion of the retina, positioning of the three beams within the patient's eye is difficult to achieve.
More particularly, a vertical disparity exists between the plane formed by the two observation beams and illumination beam as the three beams enter the pupil of the eye. Based on the portion of the eye to be observed, the distance separating the plane formed by the two observation beams and illumination beam must be varied to ensure that the three beams fit within the pupil of the eye. The maximum vertical disparity is greatest when the portion of the eye to be observed is at the center of the pupil since the shape of the pupil based on the angle at which the three beams enter the pupil is substantially circular. The maximum vertical disparity is least when the portion of the eye to be observed is at the periphery of the retina since the shape of the pupil based on the angle at which the three beams enter the pupil is substantially elliptical (i.e., the maximum vertical disparity is highly compressed).
The maximum vertical disparity is varied in the BIO U.S. Pat. No. 4,684,227 by moving the platform which supports the mirrors for reflecting the observation and illumination beams. It is difficult, however, to sufficiently reduce the maximum vertical disparity so that all three beams fit within the pupil when the peripheral portion of the eye is to be examined.
In a second type of conventional BIO, such as disclosed U.S. Pat. No 4,449,797, two mirrors are arranged on a wedge-shaped platform which can be moved towards or away from the patient's eye to adjust the position at which the observation beams enter the eye. The mirror associated with the illumination beam for adjusting the position at which the illumination beam enters the pupil is not located on the wedge-shaped platform. To adjust the position at which the observation beam enters the pupil the mirror associated with the illumination beam is rotated. In other words, similar to the BIO of U.S. Pat. No. 4,684,227, for adjusting vertical disparity, the BIO of U.S. Pat. No. 4,449,797 provides only one control for adjusting the position at which the illumination beam enters the pupil. It is therefore difficult to adjust vertical disparity with the degree of precision demanded when observing peripheral portions of the eye.
Accordingly, it is desirable to provide an improved binocular ophthalmoscope for indirect observation of an eye which has a greater range of vertical disparities as compared to a conventional binocular indirect ophthalmoscope. A higher degree of precision in vertical disparity adjustment should also be provided by the binocular ophthalmoscope.